This invention relates to an audio program control utilizing a control signal outside of the audio frequency range for controlling the operation.
Storage devices such as tape players can be readily programmed with audio frequency signals to furnish a program such as music, messages, etc., which are converted to audio sound waves through conventional speakers or the like.
Picture slide projectors have been utilized in conjunction with tape players to provide a simultaneous presentation of audio sound corresponding to the selected slide presentation, such as illustrated in the U.S. Pat. Nos. 3,420,966; 3,227,814; 3,200,206; 2,811,588; and 2,787,669. Many of such slide projectors are automatically operated by control signals generally outside of the audio frequency range which have been pre-programmed into the tape storage media for controlling the slide advance. Many of these systems employ control circuits having dual functioning elements which may be pre-conditioned to operate as a resonant or frequency selective amplifier for responding to such control signals for changing a picture slide or pre-conditioned to operate as an oscillator for selectively encoding a tape with a control signal having the desired frequency.
Teaching or instructional devices have also combined audio tape machines or recorders with slide or film projectors with the advance of such slides being controlled by frequency encoded control signals. One instructional device such as in the U.S. Pat. No. 3,664,037 employs a separate control channel in a multiple channel sound tape for supplying a high frequency film advance signal and a low frequency tape stop signal thus requiring a separate tape sensing head for sensing the control signals. Another instructional device such as in the U.S. Pat. No. 3,484,950 also employs a multiple channel tape system having a separate channel providing frequency control signals while at least one control signal is combined with audio signals and is sensed through filtering circuits for controlling the operation of the tape in combination with the control frequencies supplied from the separate control channel.